Energy Storage Device

ABSTRACT

An energy storage device comprising an anode, electrolyte, and cathode is provided. The cathode comprises a plurality of granules comprising a support material, an active electrode metal, and a salt material, such that the cathode has a granule packing density equal to or greater than about 2 g/cc. A cathode comprising greater than about 10 volume % total metallic content in a charged state of the cathode is also provided.

BACKGROUND

The invention includes embodiments that relate to an energy storagedevice. The invention includes embodiments that relate to an energystorage device with a cathode having high packing density and/or highmetallic content.

Rechargeable batteries using sodium as the negative electrode are knownin the art. Sodium has a standard reduction potential of −2.71 volts.The sodium anode may be used in liquid form, and the melting point ofsodium is 98° C. An ion conducting solid electrolyte (separator)separates the liquid sodium anode from a positive electrode (cathode).

A second, molten electrolyte transports ions to and from the separatoron the cathode side. The melting point of the molten electrolyte, alongwith the temperature-dependent, sodium-ion conductivity of the solidelectrolyte, determines the minimum operating temperature of thebattery. The cathode should include an active metal having a halidespecies that is compatible with the solid electrolyte in the charged(oxidized) state. Low solubility of the oxidized cathode material in themolten electrolyte can lead to passivation of the remaining uncharged(reduced) electrode surface and fouling of the pores.

It may be desirable to have an energy storage device that has improvedoperating life, energy density, and power density over those devicesthat are currently available.

BRIEF DESCRIPTION

In accordance with an embodiment of the invention, an energy storagedevice comprising an anode, electrolyte, and cathode is presented. Thecathode comprises a plurality of granules comprising a support material,an active electrode metal, and a salt material, wherein the cathode hasa granule packing density equal to or greater than about 2 g/cc.

In one embodiment, an energy storage device comprising an anode,electrolyte, and cathode is presented. The cathode comprises a pluralityof granules comprising brass, zinc, and sodium chloride, wherein thegranules have a multi-modal size distribution, such as, for instance, abimodal distribution. The cathode has a granule packing density in arange from about 2.0 g/cc to about 2.7 g/cc.

In one embodiment, an energy storage device comprising an anode,electrolyte, and cathode is presented. The cathode comprises a pluralityof granules comprising a support material, an active electrode metal,and a salt material, such that a total metallic content of the cathodeis greater than about 10 volume % in a charged state of the cathode.

In one embodiment, an energy storage device comprising an anode,electrolyte, and cathode is presented. The cathode comprises a pluralityof granules comprising a support material, an active electrode metal,and a salt material, such that a total metallic content of the cathodeis greater than about 10 volume % in a charged state of the cathode andthe cathode has a granule packing density equal to or greater than about2 g/cc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an electrochemical cell according to oneembodiment of the invention.

FIG. 2 is a graphical representation of cell resistances versus thestate of charge (SOC) of electrochemical cells according to oneembodiment of the invention.

FIG. 3 is a graphical representation of degradation in discharge energywith number of cycles of electrochemical cells according to oneembodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention include those that relate to anenergy storage device (such as a battery) having a cathode with highpacking density and/or a high metallic content. Embodiments also includethose that relate to the cathode, an energy storage device using thecathode, and associated methods of making the high packing densitycathode.

As used herein, an energy storage device is described using an exampleof an electrochemical cell (also denoted as “cell”). A cathode is anelectrode that supplies or receives electrons during charge/discharge ofa battery. An electrode can be used in an energy storage device. Thedevice may include a housing having an interior surface defining avolume. A separator may be disposed in the volume. The separator mayhave a first surface that defines at least a portion of a cathodechamber, and a second surface that defines an anode chamber, and thecathode chamber is in ionic communication with the anode chamber throughthe separator. An electrolyte is a medium that provides the iontransport mechanism between the positive and negative electrodes of acell, and may act as a solvent for the oxidized form of the activeelectrode metal. The ionic material transported across the separatorbetween the anode chamber and the cathode chamber can be an alkalimetal. Suitable ionic material may include one or more of sodium,lithium and potassium. The anodic material is molten during use. Theanode chamber may receive and store a reservoir of anodic material.

An electrochemical cell 100 in accordance with an embodiment is shown inFIG. 1. The cell includes a housing 102. The housing includes aseparator 104 having an outer surface 106 and an inner surface 108. Theouter surface defines a first chamber 110 and the inner surface definesa second chamber 112. The first chamber 110 is an anode chamberincluding sodium and the second chamber 112 is a cathode chamberincluding a plurality of salts. The first chamber is in ioniccommunication with the second chamber through the separator. The firstchamber 110 and the second chamber 112 further include, respectively, ananode current collector 114 and a cathode current collector 116 tocollect the current produced by the electrochemical cell. In otherembodiments, the positions of the anode 114 and cathode 116 can bereversed relative to the embodiment described above, such that the firstchamber 110 is the cathode chamber and the second chamber 112 is theanode chamber.

The cathode includes cathodic materials having differing functions, forexample, an active electrode metal, a support structure, and a saltmaterial. The active electrode metal is present in the cathode as aparticipating electrochemical reactant in its fully oxidized state orits fully reduced state, or at some state between full oxidation andreduction. The support structure supports the active electrode metal asthe active electrode metal undergoes chemical reaction and allows for asurface upon which solids may precipitate as needed. The activeelectrode metal can be disposed on to an outer surface of the supportstructure. The support structure can have a high surface area. Thesupport structure in one embodiment is an electrical conductor and alsocarries electrons to the reacting surface.

As described in above, in addition to the support structure material andactive electrode metal, the cathode comprises a salt material. The saltmaterial provides cations for conduction through the separator andhalide ions for oxidizing the metal. Thus the salt material is theprincipal source of halide ions used to produce the metal halide activeelectrode species during charging. According to one embodiment, the saltmaterials include metal chlorides. According to some embodiments, thesalt material includes sodium salts. In one embodiment, the saltmaterial is selected from the group consisting of sodium chloride,sodium bromide, and sodium fluoride. In one exemplary embodiment, thesalt material comprises sodium chloride.

The cathodic materials and an electrolyte may be disposed in a cathodechamber. At operating temperature the cathode chamber may contain activemetal, support structure, salt material, and melt of the electrolyte.

The molten salt homogeneity can be controlled by anchoring the activeelectrode metal to a support structure surface, rather than filling thecathode chamber with only a liquid melt. That is, the placement of theactive electrode metal on the support structure allows for the abilityto locate specific materials within an electrochemical cell.

In accordance with an embodiment of the invention, the support structurecomprises copper. In a further embodiment, a combination of zinc andcopper can be used as a support structure for an energy storage devicethat includes a zinc electrode. In one embodiment, the combination canbe in a mixture form. In another embodiment the zinc and copper arecombined in an alloy form. Brass is commercially available in a widevariety of compositions and may be used as a material for a supportstructure. Small amounts of other metals, such as aluminum or tin, maybe present in differing degrees based on the type and purity of brassobtained.

In one embodiment, the support structure does not undergo much, if any,chemical reaction during the charge/discharge. For example, in oneembodiment comprising copper as support structure and zinc as an activeelectrode metal, the zinc functions as a working, active electrode metalin the electrochemical cell. In another embodiment, the supportstructure participates in the chemical reaction at certain chemicalpotential. For example, in one embodiment comprising brass as thesupport material and zinc as the active electrode metal, at certainchemical potential, the zinc in the brass can also participate in thechemical reaction along with the active electrode metal. In anotherexemplary embodiment, the zinc in the brass support material itself actsas an active electrode metal and participates in the chemical reaction.

One suitable brass material may include milled brass powder that hasfrom about 20 weight percent to about 31 weight percent zinc, from about0 to about 0.9 weight percent aluminum, and the remainder copper. In oneembodiment, substantially all of the zinc in a cathodic material isalloyed with the copper to form brass. In one embodiment, the cathodicmaterial includes copper and zinc, and has less than 1 weight percent ofaluminum, tin, or aluminum and tin. In one embodiment, the amount ofaluminum or tin, or the combined amount of aluminum and tin, is in arange of from about 0.01 percent to about 0.1 percent based on theweight of the combination of copper and zinc. In one embodiment, theamount of aluminum, tin, or both is zero.

The cathodic materials may be in the form of powder, fiber, foam, orfoil. The initial form of the reactants may not be retained oncecharge/discharge cycling is complete. That is, a cell packed initiallywith powders may change to porous foam after the first or subsequentuse. The foam may be an open cell or reticulated type. In oneembodiment, the cathode is in the form of granules. The granule as usedherein means a small particle or grain. Granules can be individual or apart of a solid/semi solid structure. A granule may include the cathodicmaterials described previously, including, the support structurematerial, active electrode metal, and salt material. In one embodiment,the granules of the cathodic materials are in the form of individualpowder particles/grains in the initial state of the cathode, i.e. beforethe first use. In one embodiment, the granules are a part of the solidstructure during and after the first use of the cell. In one embodiment,at least about 75 volume % of the granules in the cell cathode comprisea support structure material, an active electrode metal, and a saltmaterial. In another embodiment, at least about 99 volume % of thegranules in the cell cathode comprise a support structure material, anactive electrode metal, and a salt material.

A cathode can have varying degrees of granule packing density, forexample, depending on the size of granules used and the method used forforming the cathode. As used herein, the “granule packing density” ofthe cathode means the mass of granules in a given volume. A cathode withhigh packing density potentially allows several possible desirableaspects. In one embodiment, the increased packing density may mean anincreased content of electrochemically active material, allowing forenhanced output energy density of the electrochemical cell relative tocathodes of lower packing density. In another embodiment, the highpacking density may result in a higher surface area compared to thecells with lower packing density within a given volume forelectrochemical action, which reduces cell polarization and therebyincreases the power of the cell. In yet another embodiment, theincreased packing density results in a better network of cathodicmaterials compared to the lower packing density cathodes, leading to auniform current distribution. A uniform current distribution allows thecell to reproducibly operate over the low-resistance pathways of thecathode, which may increase the stability, life, and predictability ofthe electrochemical cell.

According to one embodiment of the invention, the cathode of the presentinvention has a granule packing density equal to or greater than about 2g/cc. In one embodiment, a granule packing density equal to or greaterthan about 2 g/cc relates to the cathodes having equal to or above 50vol % of the granules. In another embodiment, the cathode has a granulepacking density equal to or greater than about 2.2 g/cc. In an exemplaryembodiment, the cathode has a packing density in a range from about 2.0g/cc to about 2.7 g/cc. A packing density in a range from about 2.0 g/ccto about 2.7 g/cc covers the range of about 50 vol % to 75 vol % of thegranules in the cathode, according to one embodiment. In yet anotherembodiment, the cathode has a packing density up to about 3 g/cc.

The granules can be regular-shaped, or they can have an irregular shape.In some embodiments of the invention, granules are irregular shaped.When the granules have an irregular shape, nominal size of a granulerefers to the dimension of the so-called equivalent sphere, a conceptwell-known in the field of particle size analysis.

The particle distribution of the granules can be homogeneous ornon-homogeneous. In one embodiment, the granules have non-homogeneousparticle distribution. In further embodiment, the granules have amultimodal size distribution. A multimodal size distribution is acontinuous probability distribution with multiple modes. These multiplemodes appear as distinct peaks of local maxima in a size distributioncurve. In one embodiment, the granules of cathodic materials havedistinct size ranges spanning from about 10 micrometers to about 1000micrometers. For example, the multimodal size distributed granules of acathode may comprise a mixture of distinct populations of granules withrespective median granule sizes of about 100 micrometers, about 250micrometers, and about 500 micrometers.

In a particular embodiment, the granules have a bimodal particle sizedistribution. Bimodal distribution refers to a distribution of particleswhere two local maxima are present in a size distribution. A bimodalsize distribution of granules can provide advantages such as good bulkproperties, good mixing properties, and good dissolution profiles.

In a bimodal distribution, the first mode may be in a range of fromabout 250 micrometers to about 1000 micrometers and the second mode maybe in a range of from about 10 micrometers to about 250 micrometers. Forexample, a suitable bimodal distribution may include a first mode atabout 750 micrometer granules and a second mode at about 100 micrometergranules.

In one embodiment of bimodal distribution of granules, wherein the peakheights represent the relative number of particles present in that mode,the ratio of peak height of the first mode representing larger granulesto the peak height of the second mode representing smaller granules isfrom about 90:10 to about 10:90. In another embodiment, the ratio ofpeak heights of the first mode to the second mode is from about 70:30 toabout 30:70. In another particular embodiment, the ratio of peak heightsof the first mode to the second mode is about 50:50.

The granules can be designed and formed to increase the cathodicactivity during the cell operation. One way of increasing the cathodicactivity is by increasing the surface area of the granules. Specificmethods can be used to combine the cathodic materials in the granulessuch that both the active surface area and stability of the granules areincreased. For example, in one embodiment, milled powders of supportmaterial, active cathode metal, and salt materials are individuallysieved, mixed, and compacted to ribbons using pressure. The compactionincreases the packing density of the ingredients. The compacted ribbonsmay be fractured into granules by forcing the ribbon through a screensieve for example. The granules can be classified by size and fractionsof undesirable particle size can be recycled to the start of thegranulation process.

The granules of the cathodic materials can be packed using severaltechniques to form a packed body of the cathode. For example, in oneembodiment, the multimodal size distributed granules can be compacted byvibratory packing. In another embodiment, distinctly sized monomodalgranules can be mixed and compacted using vibratory packing.

While it is desirable to have high packing density of the cathode, it isalso desirable to have a porous network within the cathode to enable theaccess of the electrolytes to the active electrode metal. Therefore,fabrication of the cathode is often driven by striking a balance betweenhigh packing density and pore surface areas of the cathode. Achieving anoptimum packing density is one way of balancing the energy density andelectrolyte access thereby optimizing the cell functions. In oneembodiment, the packing density of the cathode is in a range from about2.0 g/cc to about 2.7 g/cc.

In one embodiment, the electrolyte of the electrochemical cell has anaverage melting point of about 155 degrees Celsius (° C.). Therefore, asuitable operating temperature for the electrochemical cell of presentembodiment is above 155° C. In one embodiment, the operating temperaturefor the electrochemical cell may be greater than about 350° C.

The electrolyte may be disposed within the cathode chamber defined bythe separator. The electrolyte and the cathodic materials are compatiblewith each other and thus, in one embodiment, the cathode of the cell isoperable at a temperature greater than about 350° C. In a furtherembodiment, the cathode of the cell is operable at a temperature greaterthan about 400° C. As used herein, the term “operable” means thecapability of the cathode to operate with substantial efficiency.

The energy storage device may have a plurality of current collectorsincluding anode current collectors 114 and cathode current collectors116 as depicted in FIG. 1. The anode current collector 114 is inelectrical communication with the anode chamber 110 and the cathodecurrent collector 116 is in electrical communication with the contentsof the cathode chamber 112. Suitable materials for the anode currentcollector 114 may include W, Ti, Ni, Cu, Mo, steel, or combinations oftwo or more thereof. Other suitable materials for the anode currentcollector 114 may include carbon. The cathode current collector 116 maybe a wire, paddle or mesh formed from Pt, Pd, Au, Ni, Cu, C, Ti, W, orMo. The current collector may be plated or clad. In one embodiment, thecurrent collector is free of iron.

According to an embodiment of the invention, the cathode can exist in a“charged” state (meaning fully charged), a “discharged” state (meaningfully discharged), or in a “partially charged” state. The energy storagedevice described herein may be an electrochemical cell, assembled in thedischarged state. Applying a voltage between the anode and the cathodeof the electrochemical cell may charge the electrochemical cell. In oneembodiment, sodium chloride in the cathode dissolves to form sodium ionsand chloride ions during charging. Sodium ions, under the influence ofapplied electrical potential, conduct through the separator 104 andcombine with electrons from the external circuit to form the sodiumelectrode and chloride ions react with the cathodic material to formmetal chloride and donate electrons back to external circuit. Duringdischarge, sodium ions conduct back through the separator reversing thereaction, and generating electrons. The cell reaction is as follows:

nNaCl+M

MCl_(n) +nNa⁺ +ne ⁻

The electrochemical cell includes the separator 104 having active areaA; and the cell is capable of repeatedly storing and discharging aquantity of charge Q, the resistance between the two terminals is R; andthrough a full isothermal charge or discharge of Q, a ratio RA/Q remainsin a range of from about 1.5×10⁻⁶ ohm-m²/amp-hr to about 9.2×10⁻⁶ohm-m²/amp-hr.

The active cathode metal may exist in elemental form or as a saltdepending on a state of charge of the electrochemical cell. That is, theactive cathode metal may be present in elemental form and/or salt formand the ratio of the weight percent of the active cathode metal inelemental form to the weight percent of the salt form may be based onthe state of charge. In a charged state, the cathode may comprise lessmetallic content than in a discharged state because during charging,metals of the cathode get converted into the salt form. Duringdischarging the salt form gets converted into the metallic form and getsdeposited over the support structure material and hence the dischargedstate of the cathode will contain the maximum amount of metalliccontent. Generally, in a partially charged state, the metallic contentof the cathode will be in between the metallic content of the chargedstate and the metallic content of the discharged state.

According to one embodiment of the invention, a cathode comprising thegranules of cathodic materials has a metallic content greater than about10 volume %. A higher metallic content provides a good 3-dimensionalmetallic network in the cathode as well as a higher metal surface area,thus reducing ohmic resistance contribution in the cell resulting in ahigher power density of the cell. The high metal surface area forelectrochemical action and a better 3-dimensional metallic network alsoallows the cell to reproducibly operate over the low-resistance pathwaysof the cathode, thus increasing the stability and life of the cell.

In one embodiment, the cathode comprising the granules of cathodicmaterials has a metallic content greater than about 10 volume % in adischarged state. In certain embodiments, the granules of cathodicmaterials have a metallic content greater than about 12 volume % in adischarged state. In some embodiments, the granules of cathodicmaterials have a metallic content greater than about 15 volume % in adischarged state. In yet another particular embodiment, the granules ofcathodic materials have a metallic content up to about 23 volume %, in adischarged state.

In one embodiment, the cathode comprising the granules of cathodicmaterials has a metallic content greater than about 12 volume % in acharged state. In another embodiment, the granules of cathodic materialshave a metallic content greater than about 15 volume % in a chargedstate. In yet another particular embodiment, the granules of cathodicmaterials have a metallic content in the range up to about 18 volume %,in a charged state.

The distribution of ingredients, and therefore metallic content, neednot be homogeneous in either of the initial or the subsequent state. Aseparator 104 and cathode current collector 116, discussed furtherherein below, make reasonable reference points for a discussion of metalconcentrations. In one embodiment, in a partially charged state, thecathodic material is relatively copper rich proximate the separator 104and is relatively zinc rich proximate the current collector 116. Theratio of zinc to copper can change over the distance from the separator104 to the current collector 116 in a manner that is linear ornon-linear. In a non-linear instance, the ratio change issemi-exponential. During operation, the reaction of zinc at a firstlocation can occur prior to reacting the zinc at the second locationduring the at least one charge/discharge cycle.

According to one embodiment of the invention, an energy storage devicewith a cathode having a plurality of granules is presented. The granulepacking density of the plurality of granules in the cathode is equal toor greater than about 2 g/cc, while the total metallic content of thecathode is greater than about 10 volume % in a charged state of thecathode. In a further embodiment, the granules have a multimodal sizedistribution and a packing density greater than about 2 g/cc.

A plurality of the electrochemical cells can be organized into an energystorage system. Multiple cells can be connected in series or parallel.For convenience, a group of connected cells may be referred to as amodule or pack. The ratings for the power and energy of the module maydepend on such factors as the number of cells in the module. Otherfactors may be based on end-use application specific criteria.

A suitable energy storage system may have an application specific Powerto Energy ratio of less than 10 to 1 hour⁻¹. In one embodiment, thespecific power to energy ratio is in range from about 1:1 to about 2:1,from about 2:1 to about 4:1, from about 4:1 to about 6:1, from about 6:1to about 8:1, or from about 8:1 to about 10:1. In other embodiments, thepower to energy ratio is in range from about 1:1 to about 1:2, fromabout 1:2 to about 1:4, from about 1:4 to about 1:6, from about 1:6 toabout 1:8, or from about 1:8 to about 1:10.

The following examples illustrate methods and embodiments in accordancewith the invention, and as such do not limit the claims. Unlessspecified otherwise, all ingredients are commercially available fromcommon chemical suppliers.

Example 1 Cathode Granule Packing Density

Two batches of cathodic materials with different granule packingdensities were prepared. The solid components of a cathodic materialinclude zinc (−100 mesh, 99.9% metals basis), brass (−325 mesh, 99.9%metals basis, Cu ˜72%, Zn ˜27% by weight), sodium chloride (99.99%), andaluminum powder (−100+325 mesh, 99.97% metals basis). To increase thesurface area for improved mass transfer, the sodium chloride was milledto −200 mesh in a laboratory mill in a dry glove box. These powders weremixed and subjected to granulation.

The first batch (Batch 1) contained about 84.8 g of brass, 37.5 g ofmetallic zinc, 113.6 g of sodium chloride and 1 g of aluminum. Thesecond batch (Batch 2) contained about 102.7 g of brass, 45.5 g ofmetallic zinc, 137.6 g of sodium chloride and 1.2 g of aluminum.

Granulation was carried out in three stages. First, the mixed powderswere screw-fed to a set of rolls of a bench-top granulator having about15-mm wide rolls, and a maximum roll pressure of 120 MPa. The mixedpowders were compacted, using 120 MPa pressure and a roll speed of 4rpm, into a continuous 15 mm wide ribbon. The resulting ribbon was thenbroken up into granules by screw feeding to a 1.2-mm (16-mesh) sieve,and forcing the ribbon by a roller through the sieve. The granules werethen classified using a 300-μm sieve.

The cathodic material was disposed in the volume of the cell housing andwithin the separator tube, and functioned as the working cathode for thecell. The brass functioned as one current collector. The housingfunctioned as a second current collector. To minimize cell exposure tooxygen and moisture, the cell fabrication process was carried out in aglove box. The cell was placed on a vibratory table, and was vibrated athigh frequency for 30 s to facilitate packing of the granule bed to thedesired packing density.

Granules of size greater than about 300 μm were used for batch 1. Batch2 contained about 79 wt % of granules greater than 300 μm size and about21 wt % of granules with size less than 300 μm. The packing density ofbatch 1 was about 1.85 g/cc and that of batch 2 was about 2.24 g/cc.

The cathode compartment of the cell was charged with about 107.7 gsodium tetrachloroaluminate powder for batch 1 and about 81.6 g sodiumtetrachloroaluminate powder for batch 2. The cell was tested at 450° C.FIG. 2 graphically depicts the cell resistances in ohms of batch 1 andbatch 2 versus the state of charge (SOC) in ampere-hour (Ah) of thecells under test.

In FIG. 2, curves 202 and 204 illustrate the cell resistances of batch 1and batch 2 respectively during charge and curves 206 and 208 illustratethe cell resistances of batch 1 and batch 2 respectively duringdischarge. It can be seen from the graph that the cell resistances athigh SOC are comparatively lower for the batch 2 than batch 1 duringcharge as well as discharge. Also the cell energy at the end of 2 hourhalf cycle time during discharge for batch 2 was found to be about 64 Whcompared to about 52 Wh of batch 1. Therefore the cell of batch 2 withhigher granule packing density provides higher energy and lowerresistance compared to the cell of batch 1 having a lower granulepacking density.

Example 2 Metallic Content of the Cathode

FIG. 3 depicts the degradation in discharge energy with cycles for twobatches (Batch 3 and Batch 4) of cathodic materials with different metalcontents in the cathode granules. The materials used were the same asdescribed in Example 1 above and the contents of the cathode include51.7 g of brass, 22.9 g of metallic zinc, 69.4 g of sodium chloride and0.9 g of aluminum for batch 3 and 46.5 g of brass, 35 g of metallic zincand 62.5 g of sodium chloride for batch 4. Size of the granules used wasabout all coarse (>300 μm) for batch 3 and a mixture 30 wt % coarse −70wt % fine (<300 μm) for batch 4. The granule packing density was about1.9 g/cc for batch 3 and 2.7 g/cc for batch 4. Batch 3 has a metalliccontent of about 8.5 vol % of cathode at the end of charge (EOC) andbatch 4 had about 12.5 vol % of cathode at the end of charge. The cellswere tested at a temperature of about 430° C. Comparison of batch 3 andbatch 4 degradation densities 210, 212 in FIG. 3 shows that batch 4 witha higher metallic content of the cathode was more stable compared tobatch 3 with a comparatively lower metallic content.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. An energy storage device comprising an anode, electrolyte, andcathode, wherein the cathode comprises a plurality of granulescomprising a support material, an active electrode metal, and a saltmaterial, wherein the cathode has a granule packing density equal to orgreater than about 2 g/cc.
 2. The energy storage device of claim 1,wherein the granule packing density is in a range from about 2.0 g/cc toabout 2.7 g/cc.
 3. The energy storage device of claim 1, wherein theplurality of granules has a multimodal size distribution.
 4. The energystorage device of claim 3, wherein the multimodal size distribution is abimodal distribution.
 5. The energy storage device of claim 3, wherein afirst mode of the multimodal size distribution is less than about 250micrometers.
 6. The energy storage device of claim 5, wherein at least30 volume % of the plurality of granules in the first mode has mediansize lower than about 250 micrometers.
 7. The energy storage device ofclaim 6, wherein at least 50 volume % of the plurality of granules inthe first mode has median size lower than about 250 micrometers.
 8. Theenergy storage device of claim 3, wherein a second mode of themultimodal size distribution is greater than about 250 micrometers. 9.The energy storage device of claim 8, wherein at least 30 volume % ofthe plurality of granules in the second mode has median size greaterthan about 250 micrometers.
 10. The energy storage device of claim 9,wherein at least 50 volume % of the plurality of granules in the secondmode has median size greater than about 250 micrometers.
 11. The energystorage device of claim 8, wherein a second mode of the multimodal sizedistribution is greater than about 500 micrometers.
 12. The energystorage device of claim 1, wherein the support material comprisescopper.
 13. The energy storage device of claim 12, wherein the supportmaterial comprises zinc and copper.
 14. The energy storage device ofclaim 13, wherein the support material comprises brass.
 15. The energystorage device of claim 1, wherein the active electrode metal compriseszinc.
 16. The energy storage device of claim 1, wherein the saltmaterial is sodium chloride.
 17. An energy storage device comprising ananode, electrolyte, and cathode, wherein the cathode comprises aplurality of granules comprising brass, zinc, and sodium chloride,wherein the granules have a multimodal size distribution, and whereinthe cathode has a granule packing density in a range from about 2.0 g/ccto about 2.7 g/cc.
 18. An energy storage device comprising an anode,electrolyte, and cathode, wherein the cathode comprises a plurality ofgranules comprising a support material, an active electrode metal, and asalt material, wherein a total metallic content of the cathode isgreater than about 10 volume % in a charged state of the cathode. 19.The energy storage device of claim 18, wherein the metallic content ofthe granules is greater than about 14 volume % in the charged state ofthe cathode.
 20. The energy storage device of claim 18, wherein thesupport material comprises copper.
 21. The energy storage device ofclaim 20, wherein the support material comprises zinc and copper. 22.The energy storage device of claim 21, wherein the support materialcomprises brass.
 23. The energy storage device of claim 18, wherein theactive electrode metal comprises zinc.
 24. The energy storage device ofclaim 18, wherein the salt material is sodium chloride.
 25. The energystorage device of claim 18, wherein the cathode has a granule packingdensity equal to or greater than about 2 g/cc.
 26. The energy storagedevice of claim 25, wherein the cathode has a granule packing density ina range from about 2.0 g/cc to about 2.7 g/cc.
 27. An energy storagedevice comprising an anode, electrolyte, and cathode, wherein thecathode comprises a plurality of granules comprising a support material,an active electrode metal, and a salt material, wherein a total metalliccontent of the cathode is greater than about 10 volume % in a chargedstate of the cathode and the cathode has a granule packing density equalto or greater than about 2 g/cc.
 28. The energy storage device of claim27, wherein the granule packing density is in a range from about 2.0g/cc to about 2.7 g/cc.
 29. The energy storage device of claim 27,wherein the plurality of granules has a multimodal size distribution.30. The energy storage device of claim 29, wherein the multimodal sizedistribution is a bimodal distribution.
 31. The energy storage device ofclaim 29, wherein a first mode of the multimodal size distribution isless than about 250 micrometers.
 32. The energy storage device of claim31, wherein at least 30 volume % of the plurality of granules in thefirst mode has median size lower than about 250 micrometers.
 33. Theenergy storage device of claim 29, wherein a second mode of themultimodal size distribution is greater than about 250 micrometers. 34.The energy storage device of claim 33, wherein at least 30 volume % ofthe plurality of granules in the second mode has median size greaterthan about 250 micrometers.
 35. The energy storage device of claim 29,wherein a second mode of the multimodal size distribution is greaterthan about 500 micrometers.